U.S. patent application number 14/648826 was filed with the patent office on 2015-11-19 for velocity measurement device and velocity measurement method.
The applicant listed for this patent is SCHAFT INC.. Invention is credited to Masayuki Inaba, Jyunichi Urata.
Application Number | 20150331006 14/648826 |
Document ID | / |
Family ID | 51021015 |
Filed Date | 2015-11-19 |
United States Patent
Application |
20150331006 |
Kind Code |
A1 |
Urata; Jyunichi ; et
al. |
November 19, 2015 |
Velocity Measurement Device and Velocity Measurement Method
Abstract
The present invention aims to easily suppress noise components
of aliases when measuring a velocity based on an output from an
encoder. The invention comprises a step for converting in which
two-phase signals indicating the movement of a spinning body, etc.,
are converted to a ternary pulse train signal having a positive or
a negative or a zero value corresponding to the phases of the
two-phase signals, a step for low pass filtering in which a low
frequency component of the pulse train signal is obtained by
arithmetically processing the pulse train signal and filter
coefficients, and a step for output-sampling in which the signal
obtained by the step for low pass filtering is sampled at a
predetermined sampling period. In the step for low pass filtering,
a convolution (operation for convolution) between the pulse train
signal obtained by sampling the pulse train signal at a
predetermined period and the filter coefficients is carried out.
Sampling the pulse train signal is synchronized with and has the
same phase as reading the filter coefficients for the convolution.
The sampled signal by the step for output-sampling is output as a
velocity signal corresponding to the velocity determined by the
two-phase signal.
Inventors: |
Urata; Jyunichi; (Tokyo,
JP) ; Inaba; Masayuki; (Chiba, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SCHAFT INC. |
Tokyo |
|
JP |
|
|
Family ID: |
51021015 |
Appl. No.: |
14/648826 |
Filed: |
December 25, 2013 |
PCT Filed: |
December 25, 2013 |
PCT NO: |
PCT/JP2013/084579 |
371 Date: |
June 1, 2015 |
Current U.S.
Class: |
702/142 |
Current CPC
Class: |
G01P 3/489 20130101;
G01D 5/244 20130101; G01P 13/045 20130101 |
International
Class: |
G01P 3/489 20060101
G01P003/489; G01D 5/244 20060101 G01D005/244 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 26, 2012 |
JP |
2012-283278 |
Claims
1. A device for measuring a velocity comprising: a part for
pulse-converting that converts two-phase signals to a ternary pulse
train signal having a positive or a negative or a zero value
corresponding to phases of the two-phase signals, a low pass filter
that outputs a low frequency component of the pulse train signal by
means of arithmetical processing between the ternary pulse train
signal and filter coefficients, and a part for output-sampling that
samples the signal output from the low pass filter at a
predetermined sampling period and outputs a velocity signal
corresponding to a velocity determined by the two-phase signal.
2. The device for measuring a velocity of claim 1, wherein the
arithmetical processing at the low pass filter is a convolution
between the ternary pulse train signal and the filter coefficients,
wherein the low pass filter comprises: a counting part that
outputs, as timing signals, a readout signal having a predetermined
period, an input sampling signal synchronized with the readout
signal and having the same phase as that of the readout signal, and
an output sampling signal having the sampling period, a part for
input-sampling that samples the ternary pulse train signal based on
the input sampling signal, a part for storing filter coefficients
that stores the filter coefficients and that reads the respective
filter coefficients responding to the readout signal, a multiplexer
that outputs one of three input signals by using the ternary pulse
train signal as a signal for selection, an adder that adds a filter
coefficient read from the part for storing filter coefficients, a
subtracter that subtracts a filter coefficient read from the part
for storing filter coefficients, and a part for storing the results
that stores the results of the convolution between the pulse train
signal and the filter coefficients, wherein the multiplexer selects
a signal and outputs the selected signal from among the output
signal from the adder, the output signal from the subtracter, and
the output signal from the part for storing the results, wherein
the multiplexer selects the output signal from the adder and
outputs the output signal from the adder when the pulse train
signal is positive, selects the output signal from the subtracter
and outputs the output signal from the subtracter when the pulse
train signal is negative, and selects and outputs the output signal
from the part for storing the results when the pulse train signal
is zero, and wherein the part for storing the results samples the
output signal from the multiplexer at the sampling period and
outputs the sampled output signal from the multiplexer as a
velocity signal.
3. The device for measuring a velocity of claim 2, wherein the low
pass filter comprises an FIR filter, the counting part outputs a
reset signal having the sampling period as one of the timing
signals, the adder adds the filter coefficient read from the part
for storing filter coefficients to the output signal from the part
for storing the results, the subtracter subtracts the filter
coefficient read from the part for storing filter coefficients from
the output signal from the part for storing the results, and
wherein the part for storing the results resets the result of the
convolution at the sampling period.
4. The device for measuring a velocity of claim 2, wherein the
device comprises at least two sets of combinations of the low pass
filter and the part for output-sampling, the low pass filter in
each set receives a common ternary pulse train signal from the part
for pulse-converting, the part for input-sampling in each set
samples the ternary pulse train signal based on the input-sampling
signal that is synchronized with and has a phase different from
those in the other low pass filters, and receives the sampled
signal, the part for storing filter coefficients in each set reads
filter coefficients based on the read-out signal wherein the
read-out signal is synchronized with and has the same phase as the
input-sampling signal in the same low pass filter and wherein the
readout signal is synchronized with and has a phase different from
the input-sampling signals in the other low pass filters, the adder
and the subtracter in each set respectively adds and subtracts a
filter coefficient read from the part for storing filter
coefficients in each set, and wherein the device arithmetically
processes the output signals from the respective parts for
output-sampling in sequence or in combination, and outputs the
results.
5. A method for measuring a velocity comprising: a step for
converting in which two-phase signals are converted to a ternary
pulse train signal having a positive or a negative or a zero value
corresponding to phases of the two-phase signals, a step for low
pass filtering in which a low frequency component of the pulse
train signal is obtained by means of arithmetical processing
between the ternary pulse train signal and filter coefficients, a
step for output-sampling in which the signal obtained by the step
for low pass filtering is sampled at a predetermined sampling
period, and a step for outputting in which the sampled signal by
the step for output-sampling is output as a velocity signal
corresponding to a velocity determined by the two-phase signal.
6. The method for measuring a velocity of claim 5, wherein in the
step for low pass filtering, the ternary pulse train signal is
sampled at a predetermined period, a convolution between the pulse
train signal and the filter coefficients is carried out based on
the sampled ternary pulse train signal, in the convolution, a
filter coefficient is added when the sampled ternary pulse train
signal is positive, and a filter coefficient is subtracted when the
pulse train signal is negative, wherein reading the filter
coefficients is synchronized with sampling the pulse train signal,
and wherein in the step for output-sampling the result of the
convolution is sampled at the sampling period and output as a
velocity signal.
7. The method for measuring a velocity of claim 5, wherein the
method has a plurality of sets of combinations of the step for low
pass filtering and the step for output-sampling wherein a common
pulse train signal is input in the respective sets of the
combinations, in the same step for low pass filtering, sampling the
pulse train signal is synchronized with and has the same phase as
reading the filter coefficients for the convolution, and wherein
between the steps for low pass filtering, sampling the pulse train
signal in one of the steps is synchronized with and has a different
phase from reading the filter coefficients for the convolution in
any other of the steps.
Description
TECHNICAL FIELD
[0001] The present invention relates generally to measuring a
velocity, and more particularly to measuring a velocity based on an
output from an encoder.
BACKGROUND OF THE INVENTION
[0002] For measuring a revolving speed of a spinning body such as a
revolving shaft, using an encoder such as a rotary encoder that
outputs a signal synchronized with the revolution of the body is
well-known. For measuring a moving velocity of a linearly moving
body, using a linear encoder that outputs a signal synchronized
with the movement of the body is well-known.
[0003] FIGS. 9 and 10 are explanatory drawings showing an overall
configuration of a conventional device 101 for measuring a
velocity. By way of example, a device for measuring a revolving
speed of a spinning body is now explained. In FIG. 9, an encoder
100 outputs an output signal synchronized with the revolution of a
body such as a revolving shaft. For example, an incremental encoder
outputs two-phase output signals, i.e., an A-phase signal and a
B-phase signal (FIGS. 10a and 10b). The relationship between their
phases differs depending on the direction of the revolution. Thus,
the direction of the revolution can be detected from the
relationship between the phases of the two-phase signals.
[0004] A counting part 102 counts the signals output from the
encoder. Counting the signals can be carried out by counting the
pulses in the pulse train signal (FIG. 10c) that are obtained at
the edges of the signals output from the encoder by a counter. FIG.
10d shows a counted value.
[0005] A sampling part 103 samples counted values output from the
counting part 102 at predetermined time intervals. A part 104 for
detecting differentials outputs the temporal changing rate of the
sampled values (shown by circles in FIG. 10d) as a velocity (FIG.
10e).
[0006] Since a value obtained by counting pulses in a pulse train
signal in a predetermined period corresponds to the frequency of
the signal, measurement of such a frequency by using such a value
is well-known. The information about the frequency of the pulse
train signal is in the low frequency component in the frequency
spectrum of the value. Therefore, it is well-known to pick out the
low frequency component by eliminating the higher harmonic
component caused by a quantization error by using a low pass filter
(Patent Literature 1; Japanese Patent Publication of Examined
Application No. 2009-250807).
SUMMARY OF THE INVENTION
[0007] A conventional method generates noises such as quantization
errors when a signal output from an encoder is sampled. If a
velocity is measured based on the signal that includes the noises,
it cannot be measured with a high accuracy because the signal is
caused to fluctuate by the noise components. The quantization noise
can be eliminated by a low pass filter, because the frequency of
the noise is higher than the frequency (fi) of the pulse train
signal output from the encoder.
[0008] However, an alias-component, which is generated by sampling,
exists in a low frequency band. Accordingly, the component cannot
be eliminated by the low pass filter. FIG. 10f shows the
relationship among the frequency (f.sub.i) of the signal to be
encoded, the sampling frequency (f.sub.s), and the frequency
(f.sub.s-f.sub.i) of the alias.
[0009] Since the frequency (f.sub.s-f.sub.i) of the aliases is less
than the frequency (f.sub.i) of the signal to be encoded, a low
pass filter (LPF) cannot eliminate the frequency component of the
alias that has the frequency (f.sub.s-f.sub.i). The dashed line in
FIG. 10f shows the characteristics of the low pass filter
(LPF).
[0010] The invention of this application aims to resolve the above
problem, i.e., to easily suppress the components of a quantization
noise and an aliasing noise when a velocity is measured based on an
output from an encoder.
[0011] The invention of this application does not carry out a
conventional process in which the values got by counting the pulse
train signal are sampled and then the signal composed of the
sampled values is passed through a low pass filter. But instead it
converts a two-phase encoded signal that indicates a movement of a
spinning body to a ternary pulse train signal. Then, it directly
causes the ternary pulse train signal to pass through a low pass
filter, and obtains a velocity signal by sampling the signal having
been passed through the filter.
[0012] This invention, for measuring a velocity, causes a pulse
train signal to directly pass through a low pass filter and thus
reduces the high frequency components of the pulse train signal.
Thus, it can reduce the alias components induced by the subsequent
process for sampling the signal.
[0013] The device for measuring a velocity of this invention
comprises a part for pulse-converting that converts two-phase
signals to a ternary pulse train signal having a positive or a
negative or a zero value corresponding to the phases of the
two-phase signals, a low pass filter that outputs a low frequency
component of the pulse train signal by means of arithmetical
processing between the ternary pulse train signal and filter
coefficients, and a part for output-sampling that samples the
signal output from the low pass filter at a predetermined sampling
period and outputs a velocity signal corresponding to the velocity
determined by the two-phase signal.
[0014] The two-phase signal is an encoded pulse train obtained by
an encoder. The relationship between the phases of the two-phase
signals is the following: one of the phases is advanced or delayed
in relation to the other, depending on the direction of a movement
of an object such as the direction of a revolution. From the
relationship, the information on the direction of the revolution,
etc., can be obtained.
[0015] The part for pulse-converting converts two-phase signals to
an up and down pulse train signal having a positive or a negative
or a zero value corresponding to the relationship between the
phases of the two-phase signals. The pulse train signal can be made
by detecting the edge portions of the two-phase signals. A positive
or negative sign can be determined by the change of the
relationship between the phases of the two-phase signals.
[0016] The low pass filter is a digital filter. The filter reduces
the high frequency components in a pulse train signal, allows low
frequency components in the signal to pass through, and obtains
velocity signal components, by using an arithmetical processing
that carries out a convolution (operation for convolution) between
the pulse train signal and the filter coefficients. The part for
output-sampling samples the signal output from the low pass filter
at a predetermined sampling period. The process for causing low
frequency components to pass through the low pass filter and the
process for sampling at the part for sampling result in outputting
a velocity signal corresponding to the velocity determined by the
two-phase signal.
[0017] By the process for sampling, measuring a velocity is carried
out. That velocity corresponds to the pulse density of the pulse
train signal within a certain sampling period. The sampling period
can be arbitrarily set depending on the pulse density. For example,
if the pulse density of the pulse train signal is high and the
intervals between the pulses in a pulse train signal are short, the
pulse train signal may sharply change in a short time. In such a
case, the sampling period should be set to be short. In contrast,
if the pulse density of the pulse train signal is low and the
intervals between signals in a pulse train signal are long, the
pulse train signal cannot sharply change in a short time. In such a
case, the sampling period can be set to be long.
(An Embodiment of the Low Pass Filter)
[0018] The low pass filter carries out an arithmetical process that
picks out the low frequency component by eliminating the high
frequency component. The process carries out a convolution
(operation for convolution) between the pulse train signal and the
filter coefficients. The filter coefficients can be, say,
coefficients in a FIR filter.
[0019] The low pass filter comprises a counting part, a part for
input-sampling, a multiplexer, an adder and a subtracter, a part
for storing filter coefficients, and a part for storing the
results. The counting part outputs timing signals. The part for
input-sampling samples a pulse train signal. The multiplexer
carries out a process for selecting signals. The part for storing
filter coefficients outputs filter coefficients that are to be used
for arithmetical processing in the adder and the subtracter. The
part for storing the results stores the results of the convolution
between the pulse train signal or the result of the arithmetical
processing and the filter coefficients.
[0020] The counting part outputs a readout signal, an
input-sampling signal, and an output-sampling signal having a
sampling period, as a timing signal. The readout signal has a
predetermined cycle. The input-sampling signal is synchronized with
and has the same phase as the readout signal. The timing signal is
used for arithmetical processing, etc. Also, the counting part can
output a reset signal. The reset signal has a sampling period
synchronized with the output-sampling signal.
[0021] The part for input-sampling samples the pulse train signal
based on the input-sampling signal, and inputs the sampled signal
into the multiplexer.
[0022] The part for storing filter coefficients stores filter
coefficients that have been previously set. The part reads out the
filter coefficients when the part receives the readout signal and
then outputs the coefficients to the adder and the subtracter, so
as to set the filter coefficients for the low pass filter.
[0023] The adder adds the filter coefficients that are read out
from the part for storing the filter coefficients to the signal
output from the part for storing the results. The subtracter
subtracts the filter coefficients, which are read out from the part
for storing the filter coefficients, from the signal output from
the part for storing the results.
[0024] The multiplexer receives the pulse train signal as a control
signal for selection. Based on the signal, it outputs one of the
two signals from the adder and the subtracter, or outputs the same
signal that is output from the part for storing the results.
[0025] When the pulse train signal is positive, the multiplexer
selects and outputs the signal output from the adder, among the
signals input to the multiplexer, i.e., among the signal output
from the subtracter, the signal output from the subtracter, and the
signal output from the part for storing the results. When the pulse
train signal is negative, it selects and outputs the signal output
from the subtracter. When the pulse train signal is zero, it
selects and outputs the signal output from the part for storing the
results. This process is carried out under the condition that the
input-sampling signal is synchronized with the readout signal, and
repeated while the filter coefficients are being read out in
sequence. Thus, a convolution (operation for convolution) between
the pulse train signal and the filter coefficients is carried
out.
[0026] When a FIR filter is used, the part for storing the results
can carry out the convolution (operation for convolution) for every
sampling period, by resetting the result of the convolution at
every sampling period by using a reset signal synchronized with the
output-sampling signal.
[0027] If a FIR filter (finite impulse response filter) is
configured as a low pass filter, the counting part includes a reset
signal, as a timing signal, for resetting a sampling period. An
adder adds filter coefficients read out from a part for storing
filter coefficients to a signal output from a part for storing the
results. A subtracter subtracts filter coefficients read out from
the part for storing filter coefficients from a signal output from
the part for storing the results. A part for storing the results
resets the result of the convolution at every sampling period by
using a reset signal.
[0028] A part for output-sampling samples a signal output from the
multiplexer at every sampling period at the time of the
output-sampling signal, and outputs the sampled signal as a
velocity signal.
[0029] By the low pass filter of the invention of this application,
filter coefficients that are used for a convolution at the low pass
filter are stored in a part for storing filter coefficients.
Therefore, the coefficients can be easily changed and the change of
the characteristics of the filter can easily be made.
[0030] The low pass filter of the invention of this application is
configured to combine an adder, a subtracter, and a multiplexer. By
inputting filter coefficients to the adder or the subtracter, a
convolution between a pulse train signal and the filter
coefficients can be carried out with no multiplier.
[0031] The device for measuring a velocity of the invention of this
application has multiple sets of combinations of low pass filters,
which receive a common pulse train signal, and parts for
output-sampling. The signals that are obtained from the respective
combinations of the low pass filters and the parts for
output-sampling and that have different phases are combined and
used. Thus, the number of times of sampling can be substantially
increased and the accuracy of measurements can be increased.
[0032] The multiple sets of the combinations of the low pass
filters and the parts for output-sampling may be at least two
sets.
[0033] A common pulse train signal from the part for
pulse-converting is entered into each low pass filter in each set.
Each part for input-sampling samples the pulse train signal based
on an input-sampling signal, and then the sampled signal is output.
The input-sampling signals for the respective parts are
synchronized and have different phases.
[0034] The parts for storing filter coefficients in the low pass
filters in the respective sets read out the filter coefficients
based on the respective readout signals. The readout signal in the
same low pass filter is synchronized with and has the same phase as
the input-sampling signals. The readout signals in the different
low pass filters are synchronized with but have different phases
from the input-sampling signals.
[0035] An adder and a subtracter in each set adds or subtracts
filter coefficients read out from the part for storing filter
coefficients in the set to or from the signal output from a part
for storing results of an arithmetical process. Then the signals
output from respective parts for output-sampling are added in time
series and the result is output.
[0036] The pulse train signal is sampled by each input-sampling
signal that is synchronized with, but has different phases from,
the corresponding signals in the other sets. And each filter
coefficient is read out based on each readout signal, which is
synchronized with but has a different phase from the corresponding
signals in the other sets. The respective convolutions between the
pulse train signal and the filter coefficients are carried out.
Thus output signals having different phases are obtained. The
output signals are based on the signals that are sampled by signals
having different phases. Therefore, the output signals are
substantially equivalent to those obtained by a shorter sampling
period.
[0037] The phase-difference may be, say, a time interval obtained
by equally dividing a sampling period. For example, it may be a
half of a sampling period, or 1/3 of a sampling period.
(Method for Measuring a Velocity)
[0038] A method for measuring a velocity comprises a step for
converting, a step for low pass filtering, a step for
output-sampling, and a step for outputting. In the step for
converting, two-phase signals are converted to a ternary pulse
train signal having a positive or a negative or zero value
corresponding to the phases of the two-phase signals. In the step
for low pass filtering, a low frequency component of the pulse
train signal is obtained by means of arithmetical processing
between the ternary pulse train signal and filter coefficients. In
the step for output-sampling, the signal obtained by the step for
low pass filtering is sampled at a predetermined sampling period.
In the step for outputting, the sampled signal by the step for
output-sampling is output as a velocity signal corresponding to the
velocity determined by the two-phase signal.
[0039] In the step for low pass filtering, the pulse train signal
is sampled at a predetermined period, and a convolution (operation
for convolution) between the pulse train signal and the filter
coefficients is carried out based on the sampled pulse train
signal.
[0040] The convolution is a combination of adding and subtracting,
in which a filter coefficient is added when the ternary pulse train
signal is positive, and a filter coefficient is subtracted when the
pulse train signal is negative. Reading the filter coefficients is
synchronized with and has the same phase as sampling the pulse
train signal.
[0041] In the step for output-sampling the result of the
convolution is sampled at the sampling period and output as a
velocity signal.
[0042] A method for measuring a velocity has multiple sets of
combinations of a step for low pass filtering and a step for
output-sampling. The step for low pass filtering uses a common
pulse train signal. The outputs that have different phases and that
are obtained by the respective combinations of the steps for low
pass filtering and the step for output-sampling are combined. Thus,
the number of times of sampling can be substantially increased and
an output that is sampled by a shorter sampling period can be
obtained.
[0043] In the sets of combinations of the step for low pass
filtering and the step for output-sampling, for low pass filtering
in the same set sampling the pulse train signal is synchronized
with and has the same phase as reading the filter coefficients for
the convolution. For filtering in different sets, sampling the
signal is synchronized with but has a different phase from reading
the coefficients.
[0044] The invention of this application can be applied not only to
measuring a velocity of a spinning body but also to measuring a
velocity of a linearly moving body.
Advantageous Effects of Invention
[0045] As above, the device for measuring a velocity of this
invention does not include any integrating process. Therefore, the
device can supress quantization noises caused by integrating
quantization errors. Also, it can prevent the generation of aliases
in a process for sampling.
BRIEF DESCRIPTION OF DRAWINGS
[0046] FIG. 1 is an illustration of an outline of a device for
measuring a velocity of the invention of this application.
[0047] FIG. 2 is an illustration of the relationships between
signals in a device for measuring a velocity of the invention of
this application.
[0048] FIG. 3 is an illustration of an exemplary configuration of a
device for measuring a velocity of the invention of this
application.
[0049] FIG. 4 is an illustration of the relationships between
signals in an exemplary configuration of a device for measuring a
velocity of the invention of this application.
[0050] FIG. 5 is an illustration of a second exemplary
configuration of a device for measuring a velocity of the invention
of this application.
[0051] FIG. 6 is an illustration of a second exemplary
configuration of a device for measuring a velocity of the invention
of this application.
[0052] FIG. 7 is an illustration of an example for measuring a
velocity in accordance with the invention of this application.
[0053] FIG. 8 is an illustration of an example for measuring a
velocity in accordance with the invention of this application.
[0054] FIG. 9 is an illustration of an outline of a conventional
device for measuring a velocity.
[0055] FIG. 10 is an illustration of relationships between signals
in a conventional device for measuring a velocity.
DESCRIPTION OF EMBODIMENTS
[0056] Now, the embodiments of this invention are described in
detail, with reference to the drawings. Below, an exemplary
configuration of a device for measuring a velocity of this
invention is described, with reference to FIGS. 1-8.
[0057] FIGS. 1 and 2 are illustrations of an outline of, and the
relationships between signals in, a device for measuring a velocity
of the invention of this application. FIGS. 3 and 4 illustrate the
first exemplary configuration of a device for measuring a velocity
of the invention of this application, and the relationships between
the signals in the device. FIGS. 5 and 6 are illustrations of a
second exemplary configuration of a device for measuring a velocity
of the invention of this application. FIGS. 7 and 8 are
illustrations of an example for measuring a velocity in accordance
with the invention of this application.
(A Configuration of a Device for Measuring a Velocity)
[0058] Now, an outline of a device for measuring a velocity of the
invention of this application is described, with reference to FIGS.
1 and 2. As in FIG. 1a, in a device for measuring a velocity 1 of
the invention of this application, an encoder 10 outputs two-phase
encoded pulse train signals synchronized with a spinning body such
as a rotating shaft. One of the two-phase encoded pulse train
signals has a phase leading to, or lagging from, the other,
depending on the direction of the movement, e.g., the direction of
revolution. Based on the relationship between the phases, such
information as the direction of the revolution can be obtained.
[0059] Part 2 for pulse-converting converts the signals to an up
and down pulse train (+/- pulse train) signal that has three
values, i.e., positive, negative, and zero. For example, the pulse
train signal can be generated by detecting the edges of the
two-phase signals. The sign, i.e., positive, negative, or zero, of
the signal, can be obtained based on the change of the relationship
between the phases.
[0060] FIG. 2 has illustrations explaining the pulse-converting.
FIG. 2a shows one example of encoded pulse trains having an A-phase
and a B-phase, each of which has a different phase. There are four
relationships between the A-phase and the B-phase. FIG. 2a shows
the relationships by the numbers 1-4.
[0061] The relationship between the A-phase and the B-phase has a
different mode of shifting, depending on the direction of the
movement. FIGS. 2b and 2c show the relationships corresponding to
each direction of a revolution. FIG. 2b shows the relationships of
the phases when the spinning body is rotating clockwise. FIG. 2c
shows the relationships of the phases when the spinning body is
rotating counterclockwise.
[0062] Part 2 for pulse-converting converts the encoded pulses
having the A-phase and the B-phase to an up and down pulse train
(+/-pulse train) signal that has three values, i.e., positive,
negative, and zero. For example, when the relationship between the
A-phase and the B-phase is changed from the respective phases of
(0, 0) to those of (0, 1), a "+1" pulse is output as the pulse
train signal. In contrast, when the relationship is changed from
the respective phases of (0, 1) to those of (0, 0), a "-1" pulse is
output as the pulse train signal.
[0063] FIG. 1b shows encoded pulses and FIG. 1c shows a pulse train
signal (+/-pulse train) processed by the pulse-converting.
[0064] A low pass filter (LPF) 3 directly receives the pulse train
signal that has been converted by part 2 for pulse-converting. It
carries out an arithmetical process between the signal and filter
coefficients and allows the low frequency component that is
included in the pulse train signal to pass. Thus, it extracts a
velocity signal component. Part 4 for output-sampling samples the
signal output from the low pass filter 3 at a predetermined
sampling period. The process for allowing low frequency components
to pass through the low pass filter 3 and the process for sampling
by the part 4 for output-sampling causes a velocity signal (FIG.
1d) corresponding to the velocity indicated by the two-phase signal
to be output.
[0065] FIGS. 1e and 1f illustrate how the reductions in the alias
components differ by changing the procedures for low pass filtering
and for sampling. FIG. 1e illustrates a conventional process in
which sampling is carried out before low pass filtering is
completed. FIG. 1f illustrates a process of the invention of this
application in which low pass filtering is carried out before
sampling is done. As in FIG. 1e, if the low pass filtering is
carried out after the sampling is done, the low pass filtering
(LPF) (shown by a dashed line) cannot reduce alias components at a
frequency (f.sub.s-f.sub.i) (shown by a dotted line) generated by
the sampling.
[0066] In contrast, as in FIG. 1f, if the sampling is carried out
after the low pass filtering is done, since the low pass filter
(LPF) (shown by a dashed line) reduces certain signal components,
alias components at a frequency (f.sub.s-f.sub.i) (shown by a
dotted line) generated by the subsequent sampling can be
reduced.
(First Embodiment of the Device for Measuring a Velocity of the
Invention of this Application)
[0067] Now, the first embodiment of the invention of this
application is described, with reference to FIGS. 3 and 4. FIG. 3
illustrates the exemplary configuration of a low pass filter 3 that
is included in a device for measuring a velocity. The exemplary
configuration in FIG. 3 is a FIR filter.
[0068] The low pass filter 3 carries out a convolution (operation
for convolution) between a pulse train signal (+/-pulse train) and
filter coefficients. The filter coefficients can be, say,
coefficients in a FIR filter.
[0069] The low pass filter 3 comprises a part 3f for
input-sampling, a counting part 3e, a part 3d for storing filter
coefficients, a multiplexer 3a, an adder 3b, a subtracter 3c, and a
part 3g for storing the results. The part 3f for input-sampling
samples the pulse train signal and takes the sampled signal. The
counting part 3e outputs a readout signal having a predetermined
period, an input-sampling signal synchronized with and having the
same phase as the readout signal, an output-sampling signal having
a sampling signal, and a reset signal synchronized with the
output-sampling signal, as timing signals for arithmetic processes,
etc. The part 3d for storing filter coefficients receives the
readout signal from the counting part 3e as a timing signal and
sequentially reads out filter coefficients at a predetermined
period, and outputs them. The multiplexer 3a outputs one of three
input signals using a pulse train signal as a control signal for a
selection. The adder 3b adds the filter coefficients read out from
the part 3d to the output from the part 3g. The subtracter 3c
subtracts the filter coefficients read out from the part 3d from
the output from the part 3g. The part 3g stores the result of the
convolution between the pulse train signal and the filter
coefficients.
[0070] The counting part 3e can generate a readout signal and an
input-sampling signal having a predetermined period based on the
clock signal from a part 5 for generating a clock signal. The part
3e also can generate an output-sampling signal and a reset signal
having a sampling period.
[0071] The multiplexer 3a selects the output from the adder 3b,
i.e., the result of the addition, and outputs it, if the pulse
train signal is positive. If the pulse train signal is negative,
the multiplexer 3a selects the output from the subtracter 3c, i.e.,
the result of the subtraction, and outputs it. If the pulse train
signal is zero, the multiplexer 3a selects the value in the part
for storing the results and outputs it. The part 4 for
output-sampling receives the output-sampling signal as a timing
signal and samples the output from the multiplexer 3a. By sampling
at the sampling period, the part 4 obtains the result of the
arithmetic process for all the filter coefficients and then outputs
a velocity signal.
[0072] The part 3f for input-sampling receives the input-sampling
signal as a timing signal, samples the pulse train signal having 2
values, and sends the result to a multiplexer 3a. The part 3d for
storing filter coefficients reads out the filter coefficients that
have been stored based on the readout signal, and sends them to the
adder 3b and the subtracter 3c.
[0073] The input-sampling signal is synchronized with and has the
same phase as the readout signal. Thus, sampling the pulse train
signal and the convolution can be carried out with the same timing
as the clock signal.
[0074] The counting part 3e outputs a reset signal to a part 3g for
storing the results at a sampling period. The reset signal causes
the part 3g to start the convolution from the beginning of the
sampling period and to finish it at the end of the period. In this
way, the convolution is carried out during the sampling period,
i.e., the period is a unit for the convolution. Thus, a velocity
signal during each sampling period can be obtained.
[0075] FIG. 4a is an exemplary illustration of a pulse train signal
(+/-pulse train). A change from a positive (+1) value to a negative
(-1) value shows that the direction of movement (the direction of
revolution) has changed. FIG. 4b is an illustration of sampling
pulses that shows the period for measurements. By using those
pulses the part for output-sampling carries out the sampling.
[0076] FIG. 4c illustrates a clock signal. FIG. 4d illustrates a
readout signal and an input-sampling signal. The readout signal and
the input-sampling signal can be formed based on the clock signal.
For example, by counting a predetermined number of pulses in the
clock signal, those signals can be formed.
[0077] FIG. 4f illustrates a reset signal. FIG. 4g illustrates an
output-sampling signal. The reset signal and the output-sampling
signal are formed based on the sampling period. The reset signal is
output at the same time as the output-sampling signal. Thus, the
result of the convolution, which has been carried out during the
sampling period, can be output and then be reset.
[0078] FIG. 4e illustrates the results of the addition or the
subtraction in the convolution (operation for convolution). The
convolution carries out adding the filter coefficients to the pulse
train signal that exists within a sampling period or subtracting
the filter coefficients from the pulse train signal that exists
within a sampling period, based on whether the pulse train signal
is positive or negative. In this example, the pulse train signal
has one of two values, i.e., +1 or -1. The adder 3b sequentially
adds N+1 filter coefficients a.sub.0-a.sub.N to the output from the
multiplexer 3a or the subtracter 3c sequentially subtracts N+1
filter coefficients a.sub.0-a.sub.N from the output from the
multiplexer 3a, and then the result within the corresponding
sampling period is output.
[0079] FIG. 4h illustrates the fact that the result of the
convolution is output with the same timing as the output sampling,
i.e., at the sampling period. The output value corresponds to the
velocity signal.
(Second Embodiment of the Device for Measuring a Velocity of the
Invention of this Application)
[0080] Now, the second embodiment of the invention of this
application is described, with reference to FIGS. 5 and 6. The
second exemplary configuration is composed of a plurality of
combinations of low pass filters and parts for output-sampling. The
outputs from the respective combinations having different phases
are combined, and thus the number of times of sampling is
substantially increased. Therefore, an output that is sampled by a
shorter sampling period is obtained.
[0081] As in FIG. 5, the second exemplary configuration is composed
of a plurality of parallel combinations of low pass filters 3 and
parts 4 for output-sampling that are illustrated in the first
exemplary configuration. The pulse train signal converted by the
part 2 for pulse-converting is input to each combination of the
filter 3 and the part 4.
[0082] FIG. 5 illustrates an example that is composed of three
combinations of low pass filters 3 and parts 4 for output-sampling.
Namely, it shows the combinations of a low pass filter 3A and a
part 4A for output-sampling, a low pass filter 3B and a part 4B for
output-sampling, and a low pass filter 3C and a part 4C for
output-sampling.
[0083] In the respective low pass filters 3A, 3B, 3C, at the parts
for input-sampling, which sample a pulse train signal, the phases
of input-sampling signals are shifted so that the respective
samplings have a different timing. Also, the phases of the readout
signals are shifted so that the respective timings for reading-out
differ from each other. Then the signals that are obtained by using
those shifted phases are combined and thus the number of times for
sampling is substantially increased. If it is composed of the three
low pass filters 3A, 3B, 3C, the respective phases of the
input-sampling signals and the respective phases of the readout
signals can be shifted by 1/3 period from each other. The means for
shifting the input-sampling signals and the readout signal can use,
say, delay circuits.
[0084] The output from each part 4A, 4B, or 4C is input to a part 7
for arithmetical processing, and the part 7 outputs a velocity
signal. For example, the part 7 sequentially outputs the outputs
from the parts 4A, 4B, and 4C without modification. Or, the part 7
processes the outputs at each period for measurement in a time
series and calculates the sum or the average of the outputs at each
period.
[0085] Now, the third embodiment of the invention of this
application is described, with reference to FIG. 6. The embodiment
is composed of two parallel combinations of low pass filters 3 and
parts 4 for output-sampling.
[0086] FIG. 6 illustrates an example that is composed of two
parallel combinations, i.e., a combination of a low pass filter 3A
and a part 4A for output-sampling and a combination of a low pass
filter 3B and a part 4B for output-sampling.
[0087] The configuration of the filter 3A and the part 4A, and the
low pass filter 3B and the part 4B, in FIG. 6, is almost similar to
the configuration illustrated in FIG. 3. But the signals input to
the respective counting parts 3e differ.
[0088] The counting part 3e of the low pass filter 3A receives a
clock signal from a part 5 for generating a clock signal. Based on
the period and the phase of the signal, the part 3e generates a
readout signal and an input-sampling signal having a predetermined
period. Also, it generates a reset signal and an output-sampling
signal having a predetermined period for measurement.
[0089] The counting part 3e of the low pass filter 3B has a delay
circuit 6. The delay circuit 6 shifts the signal in the counting
part 3e of the filter 3B. Based on the phase-shifted signal, a
readout signal and an input-sampling signal are generated. Also, a
reset signal and an output-sampling signal having a predetermined
period for measurement are generated.
[0090] In accordance with the example of FIG. 6, the delay circuit
6 forms a phase difference by delaying the phase of the readout
signal and the input-sampling signal by a half period.
(An Example for Measuring a Velocity of the Invention of this
Application)
[0091] Now, an example for measuring a velocity of the invention of
this application is described, with reference to FIGS. 7 and 8.
[0092] FIG. 7a shows a pulse train output from an encoder using
counted values. FIG. 7b shows a pulse train signal (+/-pulse train)
output from a part for pulse-converting. The positive parts of the
pulse train signal correspond to the periods in which the counted
values output from the encoder are increasing. The negative parts
of the pulse train signal correspond to the periods in which the
counted values output from the encoder are decreasing.
[0093] FIG. 7c shows velocities measured by the invention of this
application and velocities measured by a conventional method. FIG.
8 shows an enlarged view of FIG. 7c.
[0094] FIG. 8a shows an example of a velocity signal that can be
obtained by the first embodiment of the invention of this
application. FIG. 8b shows an example of a velocity signal that can
be obtained by a conventional way, i.e., by detecting the
differences between sampled values. The dotted line shows the true
velocities.
[0095] The example of the velocity signal in FIG. 8 shows that
noise components caused by aliases, etc., can be significantly
suppressed compared to noise components generated in a conventional
device.
[0096] FIG. 7d shows the error between the velocity at the input
signal from the encoder and the output signal, from the measured
velocity. B shows the error obtained by a conventional device for
measuring a velocity. A shows an error obtained by a device for
measuring a velocity by using the invention of this application. By
the invention of this application, the error is found to be
decreased.
[0097] FIG. 7e shows the relationship between the error and the
velocity. The error is between the velocity measured at the input
signal from the encoder and the velocity of the output signal that
is measured. The letter B shows the relationship between the error
and the velocity, in which the measured velocity is obtained by a
conventional device for measuring a velocity. The letter A shows
the relationship between the error and the velocity, in which the
measured velocity is obtained by a device for measuring a velocity
by using the invention of this application. The horizontal axis of
FIG. 7e shows the velocity and the vertical axis shows the error.
FIG. 7e shows that by the conventional device for measuring a
velocity, the errors between the input signal and the output signal
exist independently from the velocity. In contrast, by the device
for measuring a velocity by using the invention of this
application, the errors between the input signal and the output
signal only exist where the velocity is approximately zero and the
direction of the movement is changed. The errors can be ignored
when the velocity is not zero.
[0098] The invention of this application is not limited to the
embodiments described above. It can be modified based on the
philosophy of this invention, and the modified inventions should
not be excluded from the scope of this invention.
INDUSTRIAL APPLICABILITY
[0099] The device for measuring a velocity of this application can
be applied not only for measuring a revolving speed, but also for
measuring a velocity of an object moving on a line or on a
curve.
REFERENCE LIST
[0100] 1 device for measuring a velocity [0101] 2 part for
pulse-converting [0102] 3 low pass filter [0103] 3A C3B C3C low
pass filter [0104] 3a multiplexer [0105] 3b adder [0106] 3c
subtracter [0107] 3d part for storing filter coefficients [0108] 3e
counting part [0109] 3f part for input-sampling [0110] 3g part for
storing the results [0111] 4 part for output-sampling [0112] 4A C4B
C4C part for output-sampling [0113] 5 part for generating a clock
signal [0114] 6 delay circuit [0115] 7 part for arithmetical
processing [0116] 10 encoder [0117] 100 encoder [0118] 101 device
for measuring a velocity [0119] 102 counting part [0120] 103
sampling part [0121] 104 part for detecting differentials
* * * * *